TROPICAL DISTURBANCES AND TROPICAL CYCLONES DURING POST MONSOON SEASON – An overview

Dr. S.BALACHANDRAN, Head , Regional Meteorological Centre, Chennai

MONSOON MISSION - 2019 PUNE. Semipermanent Pressure Cells and the ITCZ

July Semipermanent Pressure Cells and the ITCZ January MONSOONS

JJASSW Monsoon OND Post-Monsoon (NE Monsoon)

JULY OCT 850hPa 700hPa 200 hPa Tibetan High

TEJ (150-100 hPa)

Transient equatorial trough – LTM (1981- 2010)

TIBETAN HIGH (300hPa)

JUNE

MAY

APR Sep.

Oct.

Dec. SYNOPTIC SYSTEMS

SYNOPTIC FEATURES

 Strength of Low level easterlies off SE coast of peninsular India

 EAST – WEST ORIENTED TROUGH IN LOWER LVELS

 Formation and movement of Low Pressure Systems (LPS)

 Easterly Waves

 Tropical cyclone EASTERLY WAVES

EASTERLY WAVES

. Inverted V cloud pattern caused by convection along an easterly wave. (Balachandran , Pai1998) (Balachandran, Pai 1998) (Balachandran, Pai,1998) EW activity – NEM 2010

30-40% of seasonal rainfall during NEM 2010 was realised in association with EW acitivity

Characteristics:

Speed of movement: 7 m/s

Wavelength: 2800 km

Time period: 3-4 days

Amplitude: 6.7 m/s

(Geetha and Balachandran, 2014) EASTERLY WAVES & NEM: 13-17 Nov 2010

Associated with Nly maxima, positive OLR anomalies indicating fair weather

Hovmoller plots of meridional winds at 850 Associated with Sly maxima, negative OLR hPa & Net OLR during anomlaies indicating passage of an Ely wave active weather and over peninsular India precipitation (13-17 Nov 2010) (Geetha & Balachandran, 2014)

EW ACTIVITY

 Easterly wave activity over Indian ocean plays significant role in occurrence of the heavy rainfall events during positive phase of the ENSO; it is weak during negative phase or neutral .  Above normal SST over BOB, strong west-east SST gradient between SW BOB and tropical western Pacific ocean and anomalous strong low level easterly flow over tropical Indian ocean during El- Nino years offer favourable conditions for initiation and westward propagation of EWs. SST ANO. <-1 SD

SST ANO. > +1 SD SANAP et.al.-2018 SANAP et.al.-2018 ENSO & Post monsoon ENSO- NEM

SANAP et.al SANAP et.al Life and rainy days - MJO Phases – El Nino

P P SREEKALA et.al.-2018 Post monsoon & IOD LARGE SCALE INFLUENCES 2. INDIAN OCEAN DIPOLE (IOD)

SST anomalies are shaded (red color is for warm anomalies and blue is for cold). White patches indicate increased convective activities and arrows indicate anomalous wind directions during IOD events. 2019 –PIO-EW activity MJO & Post monsoon season MJO - NEMR

 Intraseasonal variation of daily rainfall over south peninsular India during NEM season is associated with various phases of eastward propagating MJO life cycle.

 Positive rainfall anomaly over south peninsular India and surrounding Indian Ocean (IO) is observed during the strong MJO phases 2, 3 and 4; and negative rainfall anomaly during the strong MJO phases 5,6,7,8 and 1.

 Above normal (below normal) convection over south peninsular India and suppressed convection over east Indian and West Pacific Ocean,

P P SREEKALA et.al.-2018 MJO - NEMR

 high pressure (low pressure) anomaly over West Pacific Ocean, Positive (negative) SST anomalies over equatorial East and Central Pacific Ocean and easterly wind anomaly (westerly anomaly) over equatorial Indian Ocean are the observed features during the first three MJO (5, 6, 7) phases  The number of days during the first three phases (last four phases) of MJO, where the enhanced convection and positive rainfall anomaly is over Indian Ocean (East Indian ocean and West Pacific Ocean), is more (less) during El Nino and PIOD years and less during La Nina and NIOD years and vice versa.

P P SREEKALA et.al.-2018 OLR anomalies during various MJO Phases during Oct-Dec Intra seasonal oscillations - MJO evolution

Month Week-1 Week-2 Week-3 Week-4 2018 Oct 2018 Ph:1, Ph:2, Ph:2-1 Ph:1-8 36 days in ph 2-4; Amp:>1 Amp:>1 Amp: insig Amp:1 Amp >2: 8 days Nov 2018 Ph:1-2 Ph:3-4, Ph:5-6, Ph:7, Amp:>1 Amp:>1 Amp: insig Amp:1 2015 55 days in ph 2-4; Dec 2018 Ph:1-2 Ph:3-4 Ph:4-5 Ph:5 Amp >2: 18 days Amp:>1 Amp:>1 Amp:>1 Amp:>1 Ph: 2-4, Amp>1 Favourable for enhancing NEM activity

India Meteorological Department 9 Dec SCS Pethai – MJO initiation

10 Dec

11 Dec

12 Dec

India Meteorological Department TROPICAL CYCLONES Climatology - Basins

Number of Genesis Potential Tropical Cyclones Climatology - Basins

Role of synoptic-scale forcing in cyclogenesis over the BOB Nasreen Akter • Kazuhisa Tsuboki Clim Dyn (2014) 43:2651–2662 DOI 10.1007/s00382-014-2077-9 Pre-post OHC Post-pre 600hPa RH

The higher background relative humidity during October– November than in April–May is the major factor that contributes to more frequent cyclone genesis in October– November. In contrast to the TC frequency, the most intense cyclones are observed to occur in April–May rather than in October–November. This due to the greater ocean heat content may lead to a greater TC potential intensity.

Onset Phase – Oct 2016

SW monsoon – CS KYANT (21-27th ) withdrawal upto 15N – 17th Oct

Extended SW th monsoon (till 28 ) NEM Onset - 30TH OCT (Delayed) ONSET Clustering of Tropical cyclones

Hurricane Michael Hurricane Leslie Tropical storm Nadine Hurricane sergio India Meteorological Department ENSO & TC ACTIVITY DURING NEM SEASON

TC activity over BOB is greater during La Nina years. Accumulated Cyclone Energy over NIO (1983-2008)

El Nino years ACE over BOB 1.13 kt2

La Nina years ACE over BOB 9.63 kt2

Ng & Chan, 2011 Tracks of tropical cyclones – El-Nino vs La-Nina

El Nino (1970 onwards; 8 years – La Nina (1970 onwards; 6 years- Nov-1972,77,82,87,91,94,97,2002) Nov- 1970,73,75,88,98,2000)

More westward tracks; More northward moving cyclones that Good TC activity over AS. sweep away moisture from S to N latitudes leading to suppressed NEM activity over southern India Translational Speed of CD

DECADAL VARIATIONS IN TRANSLATIONAL SPEED OF CYCLONIC DISTURBANCES OVER NORTH INDIAN OCEAN GEETHA, BALACHANDRAN MAUSAM, 65, 1 (January 2014), 115-136 Translational speed of CD

BOB ARB.

DECADAL VARIATIONS IN TRANSLATIONAL SPEED OF CYCLONIC DISTURBANCES OVER NORTH INDIAN OCEAN GEETHA,BALACHANDRAN MAUSAM, 65, 1 (January 2014), 115-136 Cyclone Rainfall Atlas- TC RAIN – WEB TOOL (based on TRMM data : 2000-2014) TC RAIN

Cyclone Rainfall Atlas- TC RAIN – WEB TOOL

TCRAIN – A DATABASE OF TROPICAL CYCLONE RAINFALL PRODUCTS FOR NORTH INDIAN OCEAN S. Balachandran et. al , DOI: 10.6057/2014TCRR02.05 Time evolution of rainfall asymmetry –VSCS MADI

Wave number 1 asymmetry shifts from front left to front right Relative magnitude of quadrant with asymmetry decrease increasing intensity. (Increase) within (beyond) 200KM as TC intensity increases. Asymmetry during recurving and looping stages w.r.t TC movement and VWS- VSCS MADI

TC MOTION

During Recurvature, there was change in orientation between VWS shear and TC motion vectors And the R/F maximum was noted in down shear – left quadrant B.Geetha and S.Balachandran* India Meteorological Department, Regional Meteorological Centre, Chennai, India Diabatic heating during Rapid intensity changes Convection asymmetry during Rapid Intensity changes TCG location variability

MJO-TC

Mohapatra ,2011 MJO-TC

Mohapatra ,2011 Future changes in tropical cyclone activity in the North Indian Ocean projected by high- resolution MRI-AGCMs

Murakami et.al Climate dynamics , 40,1949-68,2013 Summary

 The genesis, intensity and movement of tropical disturbances and Tropical cyclones during Post monsoon season play significant role in the rainfall activity over southern peninsular region.

 With increased availability of Satellite, Radar and high resolution NWP would help in further understanding of dynamics and intricacies of activity of these systems and hence improved predictive skill of NEM.

Statistical Prediction of Seasonal Cyclonic Activity over the North Indian Ocean Statistics of number of CD days during OND over NIO for the period 1971-2010.

Month Mean (days) SD (days) Oct 7.3 4.09

Nov 8.9 5.19

Dec 3.3 3.34

OND 19.57 7.99 Categorisation of No. of CD days for qualitative description of cyclonic activity

 Based on mean number of CD days (20 days) and half of the standard deviation of the number of CD days (4 days) during OND over NIO for the period 1971-2010, the following criteria is adopted for the categorisation of cyclonic activity (CA) : Category Activity  No. of CD days less than 12 : subdued CA.  No. of CD days between 12 and 16 days : below normal CA.  No. of CD days between 16 and 24 days : Normal CA.  No. of CD days greater than 24 days : above normal CA.

 Here, half of the standard deviation is considered for categorisation in order to get sufficient number of samples in each of the defined categories.

Final predictors

(i) PR1: meridional wind at 200 hPa level over 95-105˚E & 5˚S to 2˚N during August (v200,Aug)

(ii) PR2: zonal wind at 200 hPa level over 30-42˚E & 7˚S to 5˚N during August (u200,Aug)

(iii) PR3: SST over 46-56˚E & 38-34˚S during July& Aug (SST,Jul-Aug).

(iv) PR4: zonal wind at 700 hPa level over 73-80˚E & 5˚S to Equator during August (u700,Aug)

2b): v700(Aug) Regions over which the four chosen predictors PR1,PR2, PR3 and PR4 are selected.

PR2: u200(Aug) PR4:u700(Aug)

PR1:v200(Aug)

PR3:SST (Jul-Aug)